Theoretical and experimental investigation of crown/ammonium complexes in solution

Abstract

The Gibbs energies of association ΔGsolT between primary alkyl ammonium ions and crown ethers in solution are measured and calculated. Measurements are performed by isothermal titration calorimetry and revealed a strong solvent-dependent ion pair effect. Calculations are performed with density functional theory including Grimme's dispersion correction D3(BJ). The translational, rotational, and vibrational contributions to the Gibbs energy of association ΔGsolT are taken into account by a rigid-rotor-harmonic-oscillator approximation with a free-rotor approximation for low lying vibrational modes. Solvation effects δGseT are taken into account by applying the continuum solvation model COSMO-RS. Our study aims at finding a suitable theoretical method for the evaluation of the host guest interaction in crown/ammonium complexes as well as the observed ion pair effects. A good agreement of theory and experiment is only achieved, when solvation and the effects of the counterions are explicitly taken into account.

Allosteric and Chelate Cooperativity in Divalent Crown Ether/Ammonium Complexes with Strong Binding Enhancement

“…and Chiu et al . as well as our recent work demonstrated that solvation and the nature of the counterion to also have substantial effects on the association behavior of crown/ammonium complexes and the corresponding pseudorotaxanes. Hence, a solvent‐dependent analysis of ion‐pairing effects on the association processes is included here as well.…”

“…Althought he structurald ifferences of the two guests G O 2 and G C 2 are small( two ether oxygen atoms in G O 2 insteado ft wo isoelectronic methylene groups in G C 2), they differ significantly with respect to chelate cooperativity.S tudies by Gibsone tal., [39][40][41] Stoddarte tal. [42] and Chiu et al [43] as well as our recent work [44] demonstrated that solvationa nd the nature of the counterion to also have substantial effects on the association behavior of crown/ammonium complexesa nd the corresponding pseudorotaxanes. Hence, as olvent-dependent analysiso fi on-pairing effects on the association processes is included hereasw ell.…”

“…The methanol was added to improve the solubility of the charged species and to reduce ion‐pair effects, which have been reported to interfere with complex formation in solvents with low dielectric constants . Indeed, ITC studies performed in pure chloroform with the mono‐ and divalent complexes indicate that the primary ammonium ions and tosylate ions form ion pairs, which strongly interfere with the desired host–guest complex formation.…”

“…To substantiate our experimental results, DFT calculations and classical MD simulations were performed. The DFT calculations reported here follow our previously described treatment of monovalent complexes [44] to calculate the association Gibbs energies for charged monovalent crown ether/ammonium complexes in organic solvents (by using COSMO) including counterion effects (for ad etailed description of the computational methods, see the Supporting Information). [50][51][52][53][54][55][56][57][58][59][60][61] Since all ITC measurements were performed in various mixtures of chloroform and methanol, that is, solvents with low dielectric constants depending on the amount of methanol, the guest ion pairs are expected to be considerably strong.…”

A computational study of samarium diiodide‐induced cyclizations of N‐oxoalkyl‐substituted methyl indole‐3‐carboxylates—A rationale of the diastereoselectivity

“…The structures were reoptimized with PBE0‐D3/def2‐SVP. We showed in a previous study for other organic complexes that the use of a double‐ ζ basis set is sufficient for this purpose …”